/// 字符串扩展
extension StringExtension on String {
  /// 字符串首字母大写
  ///
  /// ```dart
  /// 'abc'.sl_capitalize(); // Abc
  /// ```
  String sl_capitalize() {
    if (this == null || isEmpty) return this;
    return '${this[0].toUpperCase()}${substring(1)}';
  }
}
